Extending the lifetime of NAND flash memory by salvaging bad blocks

Abstract

Flash memory is widely utilized for secondary storage today. However, its further use is hindered by the lifetime issue, which is mainly impacted by wear leveling and bad block management (BBM). Besides initial bad blocks resulting from the manufacturing process, good blocks may eventually wear out due to the limited write endurance of flash cells, even with the best wear leveling strategy. Current BBM tracks both types of bad blocks, and keeps them away from regular use. However, when the amount of bad blocks exceeds a threshold, the entire chip is rendered non-functional. In this paper, we reconsider existing BBM, and propose a novel one that reuses worn-out blocks, utilizing them in wear leveling. Experimental results show that compared to a state-of-the-art wear leveling algorithm, our design can reduce worn-out blocks by 46.5% on average with at most 1.2% performance penalties. © 2012 EDAA.